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The Role of Obstetric Ultrasound in Early Detection of Chromosomal and Structural Abnormalities


The joy when a woman becomes pregnant suddenly turns into sadness and mourning when she dies during pregnancy or childbirth, or when the baby dies. According to the World Health Organization (WHO), the five main causes of maternal deaths are bleeding, sepsis, miscarriage complications, eclampsia, and disabled birth. The World Health Organization similarly lists the most common causes of neonatal deaths as infections, birth asphyxia, birth injuries, preterm births and birth defects. It should be noted that these causes of death are those in which timely ultrasound imaging can be very helpful in early diagnosis and therefore intervention, and can lead to reduced mortality among mothers and their babies.
It is also noteworthy that most of these preventable deaths (99%) occur in developing countries where ultrasound imaging is currently inadequate and financial constraints are cited as the main cause. However, the benefit of ultrasound imaging has not been fully utilized in preventing these unnecessary deaths. It is anticipated that low resource settings can benefit from the prudent application of this modern technology, which is a relatively affordable and safe viewing method. Recently, technology has made this method so affordable and widely available that it is unacceptable to monitor such unnecessary deaths where ultrasound application can help improve survival rates.
It discusses the usefulness of ultrasound imaging at various stages of pregnancy, whether in seemingly normal or high risk situations. There is also controversy over current advances in obstetric ultrasound and imaging techniques that help improve pregnancy outcome. It also addresses the availability of more affordable yet high-quality ultrasound equipment that can improve obstetric health care, highlighting the need to implement sustainable ultrasound practice standards in developing countries where current maternal and perinatal mortality rates are unacceptably high.

Early Detection of Chromosomal and Structural Abnormalities (11-14 Week Scan)

Ultrasound imaging at the end of the first trimester for anomaly detection is typically around 11-14. It is performed to measure the nuchal translucency (NT) in weeks. NT is the ultrasound description of the subcutaneous physiological fluid collection between the skin of the fetus and the cervical spine, which can be used to obtain diagnostic information when the CRL of the fetus is 45-84 mm, GA and NT increase. The correct CRL is required to interpret the NT measurement.
NT measurement is useful in determining aneuploidy, which is an important cause of perinatal mortality. 11-14. At weeks, all major chromosome defects are associated with increased NT thickness. In a chromosomally normal fetus, increased NT thickness is also associated with major abnormalities of the heart and great vessels, diaphragmatic hernia, exomphalos, and suffocating thoracic atrophy. Therefore, further sonographic evaluation with echocardiography or 3D imaging may be requested to rule out these abnormalities. Other defects that can be detected during this pregnancy period are: acrania, anencephaly, encephalocele, gastroschisis, cleft palate, etc. The Role of Obstetric Ultrasound in Early Detection of Chromosomal and Structural Abnormalities
The role of ultrasound imaging in the early prediction of aneuploidy and structural defects reduces the number of perinatal deaths from birth defects as it offers the opportunity to decide whether to terminate the double chromosomally abnormal fetus. Termination of pregnancy at this early pregnancy is associated with less maternal morbidity and mortality.
In developed countries, early termination of a chromosomally abnormal fetus has significantly reduced perinatal mortality and may be beneficial in developing countries; Because with increasing education, women in these countries now give birth later in their lives, putting them at risk of having chromosomally abnormal babies.
Invasive prenatal tests with amniocentesis or chorionic villous sampling, which are necessary for definitive diagnosis, also require ultrasound guidance. This invasive procedure can unfortunately result in a normal pregnancy miscarriage. The important role of ultrasound is therefore based on the fact that most fetuses with chromosomal abnormalities have either major structural malformations or small abnormalities (markers) that can be detected sonographically at this early stage of pregnancy and make termination possible. (pregnancy with less morbidity and mortality)The Role of Obstetric Ultrasound in Early Detection of Chromosomal and Structural Abnormalities
Even if the couple decides to continue the pregnancy, knowledge of structural defects allows them to be referred to a tertiary center to improve postnatal care. Based on the reported findings of Nicolaides, it shows the first trimester anomalies (markers) associated with aneuploidy. Although NT can be accurately measured with TAS in approximately 95% of cases, a combination of TAS and TVS is required in cases involving TAS assessment of NT and structural abnormalities. TAS’s advantage is that it allows flexibility of probe manipulation. However, TVS offers better resolution and visualization.
In a study by Braithwaite et al. Comparing fetal anatomy using TVS and TAS at 12 to 13 weeks, they found that a complete anatomy search was possible in 72% of women using TAS, 82% with TVS, and 95%. Additional sonographic findings obtained by M-mode assessment of fetal heart rate are also useful for predicting aneuploidy on ultrasound imaging in the late first trimester. The normal fetal heart rate (FHR) increases from about 100 bpm at the 5th week of pregnancy to 170 bpm at the 10th week and then decreases to 155 bpm at the 14th week (Nicolaides et al., 2004). 10-14. At weeks trisomy 13 and Turner syndrome are associated with tachycardia, while trisomy 18 and triploidy are associated with fetal bradycardia. There is a slight increase in FHR in trisomy 21.The Role of Obstetric Ultrasound in Early Detection of Chromosomal and Structural Abnormalities
The rate of detection of additional structural abnormalities, some of which researchers have listed, depends on the skill and experience of the sonographer and to a lesser extent on the machine. Many structural abnormalities have been detected in recent years with the latest technology ultrasound machine. In five separate studies about screening an unselected population in the first trimester, fetal abnormality detection rates range from 33% to 64.7%. The importance of 3D ultrasound imaging, especially in high-risk families, further increases the detection of the abnormality. Some researchers have suggested that 3-D ultrasound imaging is the preferred tool for evaluating skeletal structures and thorax, especially long bones, due to its ability to rotate volumes.
However, the rapid movement of the fetus and the positioning of the extremities adjacent to the uterine wall could potentially be an obstacle to their assessment. Although 4-D imaging has proven to be more useful, the primary stumbling blocks remain the same. Despite increasing technological advancement, including ultrasound imaging, maternal and perinatal mortality has not decreased globally and indeed has been on the rise in some developing countries. Major causes of maternal deaths include abortion-related complications, bleeding from various conditions, hypertensive disorders, thromboembolism, obstructed labor, prolonged labor, ruptured uterus and puerperal infection. Perinatal death causes include prematurity, birth asphyxia, congenital malformations, IUGR, traumatic delivery and cord prolapse. An important part of these conditions that cause maternal death also lead to perinatal death.
Fortunately, ultrasound is a non-invasive and safe tool that can help diagnose most of these conditions, prevent the effects of these complications, and in some cases guide treatment. Therefore, wider use of ultrasound in obstetric practice is advocated. It is important to educate every medical doctor and even midwives in the obstetrics unit in the basic use of ultrasound in obstetrics. The need for advanced practice training for professional sonographers as sonologists and advanced ultrasound practitioners is recommended in the future in developing countries, as is currently practiced in some developed countries.
Governments must be committed to the purchase and maintenance of ultrasound machines for healthcare facilities, especially in obstetric units. The wider use of ultrasound imaging and the improvement in the treatment approach should lead to a decrease in maternal and perinatal mortality.

References:
https://www.glowm.com/section-view/heading/ultrasound-diagnosis-of-fetal-anomalies/item/205
http://cms.galenos.com.tr/Uploads/Article_16802/JTGGA-19-142-En.pdf
https://www.glowm.com/section-view/heading/ultrasound-diagnosis-of-fetal-anomalies/item/205

Writer: Ozlem Guvenc Agaoglu


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